The present invention generally relates to a system and method for mitigating wafer surface disformation during chemical mechanical polishing (CMP).
Traditionally, integrated circuits are built upon a flat disk crystal silicon substrate referred to as a blank silicon wafer. The surface of the wafer is subdivided into a plurality of rectangular areas on which are formed photolithographic images.
The ever increasing demand for miniaturization in the field of integrated circuits results in a corresponding demand for increased device density. Moreover, market forces are creating a need to improve device yield per wafer. As a result, larger wafers are being used to yield more devices per wafer. Chemical mechanical polishing (CMP) of is often employed in integrated circuit manufacture. The chemical mechanical polishing is typically performed to remove unwanted protrusions from a surface of the wafer, planarize a surface of the wafer and/or remove a predetermined thickness of a layer on the wafer.
One undesirable consequence of performing CMP on large size wafers is dishing and/or bowing of the wafer surface as a result of differing pressure gradients during CMP. Prior art FIG. 1a illustrates a wafer 10 that has been disformed by a CMP process so as to dish as a result of differing pressure gradients during CMP. Prior art FIG. 1b illustrates a wafer 12 that has been disformed by a CMP process so as to bow as a result of differing pressure gradients during CMP. Such dishing or bowing of the wafer is undesirable because it contributes to non-uniformity of integrated circuits formed from the wafer, and/or device defects.
Accordingly, there is a need for a solution to mitigate wafer disformation.
The present invention provides for a system and method for mitigating wafer disformation during chemical mechanical polishing (CMP). In accordance with a preferred embodiment of the present invention, two or more polishing pads are employed to concurrently polish a wafer surface. Each pad is applied at a different pressure so as to minimize differing pressure gradients during CMP. A feedback system is employed in connection with each pad to facilitate determining the thickness of the region of material being polished by each pad respectively. The feedback information is employed to adjust the pressure of the respective pads so as to mitigate disformation of the wafer during CMP.
One particular aspect of the present invention relates to a system for mitigating wafer disformation. The system includes at least a first polishing pad and a second polishing pad for polishing a wafer surface. A CMP drive system selectively applys the first and second polishing pads against the wafer surface at first and second pressures, respectively. A measuring system measures a wafer surface thickness associated with a first circumferential region of the wafer polished by the first polishing pad and a wafer surface thickness associated with a second circumferential region of the wafer polished by the second polishing pad. A processor employs information from the measuring system to control the CMP drive system.
Another aspect of the present invention relates to a system for mitigating wafer disformation. At least a first polishing pad and a second polishing pad polish a wafer surface. The system includes a first optical waveguide associated with the first polishing pad and a second optical waveguide associated with the second polishing pad. A CMP drive system selectively applies the first and second polishing pads against the wafer surface at first and second pressures, respectively. A measuring system measures a wafer surface thickness associated with a first circumferential region of the wafer polished by the first polishing pad and a wafer surface thickness associated with a second circumferential region of the wafer polished by the second polishing pad. A processor employs information from the measuring system to control the CMP drive system.
Yet another aspect of the present invention relates to a system for mitigating wafer disformation, including: at least a first polishing pad and a second polishing pad for polishing a wafer surface; means for selectively applying the first and second polishing pads against the wafer surface at first and second pressures, respectively; means for measuring a wafer surface thickness associated with a first circumferential region of the wafer polished by the first polishing pad and a wafer surface thickness associated with a second circumferential region of the wafer polished by the second polishing pad; and means employing information from the measuring system to control the means for selectively applying the first and second polishing pads against the wafer surface at first and second pressures.
Still yet another aspect of the present invention relates to a system for mitigating wafer disformation, including: a polishing pad for polishing a wafer surface; a CMP drive system for selectively applying the polishing pad against a first circumferential region of the wafer surface at a first pressure and applying the polishing pad against a second circumferential region of the wafer surface at a second pressure; a system for measuring a wafer surface thickness associated with the first circumferential region and a wafer surface thickness associated with the second circumferential region of the wafer; and a processor for employing information from the measuring system, the processor employing the information to control the CMP drive system.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.